Compressive forming

ABSTRACT

1. Apparatus for the compressive forming of an article comprising: A DIE INCLUDING A. A DIE CAVITY, B. A WORKPIECE RECEIVING CHAMBER CONNECTED WITH AND ANGULARLY DISPOSED WITH THE DIE CAVITY AND C. PORT MEANS IN A WALL OF THE DIE CAVITY AND DISTINCT FROM THE WORKPIECE RECEIVING CHAMBER; A SOFT METAL MATRIX CONTAINED WITHIN THE DIE CAVITY; MEANS TO INTRODUCE A WORKPIECE INTO THE DIE CAVITY; FORCE MEANS TO PRESS THE WORKPIECE INTO THE DIE CAVITY; AND CONTROL MEANS TO CONTROL THE RATE OF RELEASE OF MATRIX FROM THE DIE CAVITY THROUGH THE PORT MEANS.

United States Patent 1 Cogan I 1 *Aug. 7, 1973 COMPRESSIVE FORMING [75] Inventor: Richard Cogan, Hamilton, Mass.

[73] Assignee: General Electrlc Company,

Cincinnati, Ohio 211 App]. No.: 245,734

[52] US. Cl 72/57, 72/352, 72/354, 72/358, 72/60 [51] Int. Cl B2ld 39/08 [58] Field of Search 72/54, 57, 60, 343, 72/352, 354, 362, 357, 361, 353, 6

[56] 0- References Cited UNITED STATES PATENTS 1,012,401 12/1911 McCullough 72/57 1,613,595 1/1927 Abel 72/353 2,168,641 8/1939 Arbogast.... 72/354 2,783,727 3/1957 Hoffmann 72/57 Primary Examiner-Charles W. Lanham Assistant ExaminerLowell A. Larson Attorney-L. H. Sachs, E. L. Lee, 111 and Derek P.

Lawrence EXEMPLARY CLAIM 1. Apparatus for the compressive forming of an article comprising:

a die including a. a die cavity, b. a workpiece receiving chamber connected with and angularly disposed with the die cavity and c. port means in a wall of the die cavity and distinct from the workpiece receiving chamber; a soft metal matrix contained within the die cavity; means to introduce a workpiece into the die cavity; force means to press the workpiece into the die cavity; and control means to control the rate of release of matrix from the die cavity through the port means.

4 Claims, 12 Drawing Flgures COMPRESSIVE FORMING This invention relates to the forming of articles through the use of compressive forces, and more particularly, to methods and apparatus for use in the compressivc forming of solid metallic articles.-

Various types of extrusion processes wherein relatively ductile materials such as metals are pressed, forged or extruded by means of dies are well known in the art of metal working. For example US. Pat. No.

1,613,595 Abel shows the forging of a blank into an article through the use of appropriately shaped dies into which the blank is pressed. In such US. Pat. Nos. as 2,027,285 Parker and 2,243,809 Wendel, a compressive force, sometimes transmitted to the workpiece through a liquid is applied inside a hollow work piece to press portions of the workpiece into a die member. The die may or may not include a type of guiding means to adjust the shape of the expanding wall. Furthermore, various drop forging and roll forming methods are widely described in the literature. In all of these known methods and with the use of known machining and grinding, are required; In addition, the

more ductile metals cannot be formed into more complex shapes, such as turbine blades and wheels for prop'ulsion apparatus, in substantially a single step through the use of k-hown methods.

A number of experiments in the field of the fracturing of metals has shown that the application of external pressure through a liquid to a metallic material during working, such as in a tensile test, results in a great increase in ductility. Typical examples are reported in Studies in Large Plastic Flow and Fracture by P. W. Bridgman in the Metallurgy and Metallurgical Series published by McGraw Hill Book Company, Inc. in 1952.

It is a principle object of this invention to provide an improved method for compressive forming of an article in a shaped die cavity through the application of controlled back pressure to the deforming portion of a workpiece.

Another object is to provide an improved apparatus, including a die cavity in which a workpiece is formed and in which the application of back pressure to the deforming portion of a workpiece can be controlled and programmed.

These and other objects and advantages will be more readily recognized from the following detailed description and the drawing in which:

FIGS. 1 3 are sectional, partially schematic views of one form of the die of the present invention in operation;

FIGS. 4 and 5 are sectional, partially schematic views of another form of the die of the present invention in operation;

FIGS. 6, 7 and 8 are sectional, isometric, partially schematic views of other forms of the apparatus of the present invention;

FIGS. 9, l0 and 11 are sectional, partially schematic views of still another form of the present invention; and

FIG. 12 is sectional, isometric view ofa whwlformed by the apparatus in FIGS. 9 11.

Briefly, the present invention in one of its method forms for compressively forming articles in a die cavity comprises the steps of filling the die cavity with a matrix, and then pressing a workpiece into the die cavity with a material or workpiece deforming force while at the same time releasing the matrix from the die cavity at'a controlled rate as a result of the deforming portion of the workpiece displacing and transmitting, pressure to the matrix at the same time a reaction back pressure is exerted by the matrix on the workpiece. In a preferred form, the rate of matrix flow from the die cavity is controlled so that a reaction force is applied to the deforming workpiece at the interface between the matrix and the workpiece of a magnitude of at least threequarters of the compressive strength of the material of the workpiece.

The apparatus form of the present invention in one aspect includes a die having a die cavity. Connected with the die cavity are a workpiece'receiving chamber and port means. The apparatus includes means to introducea matrix into the die cavity and means to intro- ,duce a workpiece into the die cavity, force means to press the workpiece intothe die cavity, and control means to control the rate of matrix release from media cavitythrough the port means. 7

The practice of the'present invention will eliminate the hot forming and cladding required to be used with many advanced materials. It will allow cold forming of highly reactive materials such as those reactive to oxidation and to conventional forging temperatures. For

example, such materials as beryllium, tungsten, columbium and molybdenum could be cold formed in the M clad condition. In addition, brittle alloys such as the nickel base superalloys, cast iron, etc., which are now used only in the cast condition becauseof their relatively poor ductility have been worked by the method of the present invention to result in superior strength as a result of the improved grain size and flow characteristics developed by the present invention. This method is applicable as well to conventional, more ductile alloys to prepare in a single operation more complex forging shapes than can be prepared by present processing thus eliminating finishing operations and costs.

The use of ultra high pressure equipment for deforming metals has been reported in the literature. One such article appeared in Mechanical Engineering published by the American Society of Mechanical Engineers, October 1961, at pages 37 43. The present invention contemplates the use of such equipment to apply the forces represented schematically by the various arrows in the drawing. Furthermore, the die technology such as the concentric interferring ring concept shown in that article can be used with the present invention with the significant modifications shown in the drawings particularly with regard to matrix release.

In the drawing, FIGS. 1 3, inclusive, represent a sequence using the apparatusof this invention, in the practice of its method aspect, to form a billet 20, FIG. 1 into a shaped disc 20a in FIG. 3.

In FIG. 1, a die 24 having a cavity 26 shaped according to the article to be compressively formed is first filled with a matrix 28. A billet 20, introduced through workpiece receiving chamber 22, contacts matrix 28 at interface 32. The material of matrix 28 is one which has a compressive strength less than that of the material of billet 20. Compressive strength is defined, with regard to yield, as the maximum stress that a material subjectcd to compression can withstand without a predefined amount of plastic deformation. Therefore, the material of matrix 28 will flow at a pressure lower per unit than will the material of billet 20.

Die 24 is provided with release or port means 30 through which the matrix 28 can flow. Port means 30 can be of a predetermined size or can include valve means, such as 42 in FIG. 6, to control the rate of flow of matrix 28. This arrangement provides a predetermined pressure inside cavity 26, particularly at interface 32 between the workpiece billet and the matrix 28. The size and shape of cavity 26 can be maintained uniformly throughout the process either by means of externally applied force such as is represented by arrows 34, or by the construction and resistance to deformation of the material of the die itself in comparison with the magnitude of the forces applied inside the die during processing.

In the process shown in FIGS. 1 3, a workpiece deforming force, represented by arrow 36 is applied to the workpiece billet 20 to press the workpiece into the die. The minimum amount required for force 36 is the sum of l) a force equal to the compressive strength of the material of billet 20 under ordinary yield conditions, (2) a force predetermined to press matrix 28 through port 30 and (3) a friction force resisting flow of the workpiece in the die. It has been found that the application of back pressure on the deforming interface 32 of workpiece 20 by a matrix 28 preloaded into the die cavity inhibits the start of cracking of the workpiece material at that interface and allows a much greater deformation of workpiece 20 than could be achieved under normal extrusion type conditions. It has been found, in addition, the the preferred amount of back pressure exerted by the matrix on workpiece 20 is at least about three-quarters of the compressive strength of the workpiece material. Although greater rates of workpiece deformation can be achieved when the back pressure is less than that amount, at such lower back pressures, there is a substantial increase in the possibility of producing cracks in the area of interface 32.

As workpiece deforming force 36 is applied to workpiece 20, FIG. 2, the material of workpiece 20 is deformed plastically into die cavity 26 when matrix 28, under pressure of force 36, begins to flow through port 30. However, at the same time, the matrix is exerting back pressure on the workpiece at interface 32. When all of the matrix has been released from die cavity 26, as shown in FIG. 3, the material of workpiece 20 has assumed in a single operation the desired shape of article 20a. Because the material in the workpiece has been under proper and continuous controlled back pressure from the matrix 28, no cracks exist in the article 20a which is as accurate dimensionally as is die cavity 26.

As shown in FIGS. 4 and 5, the operation and apparatus in FIGS. 1 3 can be modified according to this invention to provide the application of force 36 to workpiece 20 from a plurality of directions in order to control the flow of workpiece material. The matrix 28 is controlled and released in the same manner as described in connection with FIGS. 1 3.

The phenomenon of increased ductility of metallic materials in a hydrostatic environment such as exists in die cavity 26 during operation of the present invention could be explained by the theory that such high pressure prevents the formation of voids about discontinuities or internal flaws in the material. Research has shown that such voids and flaws act as points of fracture initiation. Another possible explanation is that high hydrostatic pressure repairs, by pressure welding minute fractures occurring in materials being deformed.

In some instances, particularly those involving the formation of complex shaped articles such as a ships propeller, it is desirable to control the flow of matrix from the die cavity in a manner which will better guide the flow of the workpiece material to its finished shape in the die. As shown in FIG. 6, a plurality of ports 30 can be appropriately located in die 40 to guide further the flow of the workpiece material by means of the release of matrix 28 from the die cavity 26. A manifold 38 can be provided with die 40, as in FIG. 6, to control back pressure while allowing ports 30 to control flow rates. Means to control theflow of matrix from manifold 38 can be provided by one or a plurality of ports 30a which can include valves 42 in the ports or in con nection with manifold -38 to control ultimately the back pressure applied to interface 32 of workpiece material 20. Programming the passage of matrix 28 through a plurality of valves 42 can provide accurate control of workpiece material flow.

FIGS. 7 and 8 represent anotherform of the present invention using split die halves 44 and 44a held together by external forces 46 such as a mechanical press. External force 46 cooperates with and is less than workpiece deforming force 36 per unit of area. Upon application of force 36, the dies 44 and 44a will separate to create aport means 48 to allow matrix 28 to be extruded or released. In this case, port 48 is an annular slot. The relationship of workpiece deforming force 36 to force 46 determines the separation distance between die halves 44 and 44a and hence the size of port 48. These two forces can be varied to control the rate of flow and the back pressure of matrix 28 on the deforming interface 32 between matrix 28 and the material of workpiece 20..

The present invention can be used to make a wheel for an axial flow compressor stage having a central opening for mounting the wheel on a shaft. Such a wheel is shown in FIG. 12. A ring forging 50 in FIG. 9 can be used with the method. and apparatus of this invention shown in FIGS. 9, l0 and 11 in the manner described above. As is seen in FIG. 10, the workpiece material 50 of each portion of the ring is deformed in two directions at the same time with the matrix being released through a plurality of ports such as 52 and 54. Furthermore, the concept shown in FIGS. 4 and 5 involving the application of force from ,a plurality of di-. rections to each portion of the workpiece can be applied to the operations of FIGS. 9, l0 and 11 within the scope of this invention to form an article such as shown in FIG. 12.

The matrix material preloaded into and cooperating with the die cavity is a material more ductile or having a lower compressive strength than that of the material of the workpiece and of the material of the die. Such a ductile matrix material, is preferably based on such elements as lead, copper, zinc and other soft, easily ex truded materials. However less ductile materials can be used provided the die material can withstand the total compressive forces required through the use of a matrix more difficult to flow.

The matrix material which fills the die cavity prior to operation can be introduced in a variety of ways. However successful operation has resulted by forcing a matrix such as lead, under substantial pressure into the cavity by a ram through the workpiece receiving port until the cavity is filled. Then the workpiece material is placed in the workpiece receiving cavity in contact with the matrix and the above described process of pressing the workpiece material into the die takes place with the more ductile matrix being displaced by the workpiece flowing into the die cavity. As was mentioned above, the back pressure exerted by the matrix depends upon the matrix material used, the rate at which the matrix was displaced, and the size and shape of the port or the control exercised by the valve in connection with the port. The back pressure, sometimes referred to as hydro dynamic pressure, can be controlled by these variablesto suit the requirements of the workpiece material and the shape of the article being formed. i

As was mentioned above, it has been theorized that ductile tensile fractures begin with the formation of extremely small voids, concurrent with plastic slip. The present invention supplies forces by back pressure to effectively prevent these voids from forming or opening. In addition, the back pressure applied by the matrix results in uniform strain distribution in the compressively formed article. Under normal open die forging methods, the non-uniform strain distribution arising from die friction results in a complex distribution of stresses in the article from its center to its edge. Such a distribution can lead to cracking at the edges because of the development of high-tensile hoop stresses. The low yield stress of the matrix as used in the present invention limits the effect offriction and produces a more homogeneous distribution eliminating cracking by controlling the strain rate of the workpiece material.

Although the present invention has been described in connection with specific examples and embodiments, those skilled in the arts involved will understand the modifications and variations of which the invention is capable within its broad scope.

What is claimed is:

1. Apparatus for the compressive forming of an article comprising:

a die including a. a die cavity,

b. a workpiece receiving chamber connected with and angularly disposed with the die cavity and c. port means in a wall of the die cavity and distinct from the workpiece receiving chamber;

a soft metal matrix contained within the die cavity;

means to introduce a workpiece into the die cavity;

force means to press the workpiece into the die cavity; and

control means to control the rate of release of matrix from the die cavity through the port means.

2. Apparatus for use in the compressive forming of an article comprising:

a die including a. a plurality of shaped members which together define walls of a die cavity and b. a workpiece receiving chamber connected with and angularly disposed with the die cavity;

a soft metal matrix contained within the die cavity;

means to introduce a workpiece into the die cavity through the workpiece receiving chamber;

a first force means to press the workpiece into the die cavity;

second force means to press the plurality of shaped members one toward the other;

the first force means being greater than the sum of the second force means and the compressive strength of the workpiece material;

whereby the first force means deforms the workpiece into the die cavity while at the same time separating the walls of the plurality of shaped members to allow matrix to flow from the walls of the die cavity.

3. A method for compressively forming a workpiece into an article in a die having a cavity shaped as the article to be formed, comprising the steps of:

filling the die cavity with a soft metal matrix having a compressive strength less than that of the workpiece and of the die; and then pressing the workpiece into the die cavity and against the matrix with a workpiece deforming force to elongate and form the workpiece into the article in the die cavity, while at the same time,

releasing from walls of the cavity the matrix displaced by the forming workpiece,

the matrix being released at a controlled rate to control pressure exerted at the interface between the workpiece and the matrix to at least about threefourths of the compressive strength of the workpiece.

4. A method for compressively forming a workpiece into an article in a die having a workpiece receiving chamber and a die cavity shaped as the article to be formed, comprising the steps of:

filling the die cavity with a solid soft metal matrix having a compressive strength less than that of the die and of the workpiece;

introducing a workpiece into the workpiece receiving chamber;

applying a material deforming force to the workpiece to press the workpiece into the die cavity and against the matrix to elongate and form the workpiece into the article in the die cavity while at the same time,

releasing from walls of the die cavity the matrix displaced by the forming workpiece,

the matrix being released at a controlled rate to control pressure exerted at the interface between the matrix and the workpiece to at least about threefourths of the compressive strength of the workpiece.

III II III 

1. Apparatus for the compressive forming of an article comprising: a die including a. a die cavity, b. a workpiece receiving chamber connected with and angularly disposed with the die cavity and c. port means in a wall of the die cavity and distinct from the workpiece receiving chamber; a soft metal matrix contained within the die cavity; means to introduce a workpiece into the die cavity; force means to press the workpiece into the die cavity; and control means to control the rate of release of matrix from the die cavity through the port means.
 2. Apparatus for use in the compressive forming of an article comprising: a die including a. a plurality of shaped members which together define walls of a die cavity and b. a workpiece receiving chamber connected with and angularly disposed with the die cavity; a soft metal matrix contained within the die cavity; means to introduce a workpiece into the die cavity through the workpiece receiving chamber; a first force means to press the workpiece into the die cavity; second force means to press the plurality of shaped members one toward the other; the first force means being greater than the sum of the second force means and the compressive strength of the workpiece material; whereby the first force means deforms the workpiece into the die cavity while at the same time separating the walls of the plurality of shaped members to allow matrix to flow from the walls of the die cavity.
 3. A method for compressively forming a workpiece into an article in a die having a cavity shaped as the article to be formed, comprising the steps of: filling the die cavity with a soft metal matrix having a compressive strength less than that of the workpiece and of the die; and then pressing the workpiece into the die cavity and against the matrix with a workpiece deforming force to elongate and form the workpiece into the article in the die cavity, while at the same time, releasing from walls of the cavity the matrix displaced by the forming workpiece, the matrix being released at a controlled rate to control pressure exerted at the interface between the workpiece and the matrix to at least about three-fourths of the compressive strength of the workpiece.
 4. A method for compressively forming a workpiece into an article in a die having a workpiece receiving chamber and a die cavity shaped as the article to be formed, comprising the steps of: filling the die cavity with a solid soft metal matrix having a compressive strength less than that of the die and of the workpiece; introducing a workpiece into the workpiece receiving chamber; applying a material deforming force to the workpiece to press the workpiece into the die cavity and against the matrix to elongate and form the workpiece into the article in the die cavity while at the same time, releasing from walls of the die cavity the matrix displaced by the forming workpiece, the matrix being released at a controlled rate to control pressure exerted at the interface between the matrix and the workpiece to at least about three-fourths of the compressive strength of the workpiece. 